Field of the Disclosure
The present disclosure relates to an image forming apparatus employing an electrophotographic method, such as a laser printer, a copying machine, or a facsimile machine.
Description of the Related Art
Conventionally, in a color image forming apparatus employing an electrophotographic method, an intermediate transfer method is used for sequentially transferring toner images from image forming units of respective colors onto an intermediate transfer member and further collectively transferring the toner images from the intermediate transfer member onto a transfer material.
In such an image forming apparatus, the image forming units of the respective colors include drum-like photosensitive members (hereinafter referred to as “photosensitive drums”) as image bearing members. As the intermediate transfer member, an intermediate transfer belt formed of an endless belt is widely used. Toner images formed on the photosensitive drums of the respective image forming units are primarily transferred onto the intermediate transfer belt by a primary transfer power supply applying a voltage to primary transfer members provided opposed to the photosensitive drums through the intermediate transfer belt. The toner images of the respective colors primarily transferred from the image forming units of the respective colors onto the intermediate transfer belt are collectively secondarily transferred from the intermediate transfer belt onto a transfer material such as paper or an overhead projector (OHP) sheet by a secondary transfer power supply applying a voltage to a secondary transfer member at a secondary transfer portion. The toner images of the respective colors transferred onto the transfer material are then fixed to the transfer material by a fixing unit.
In the image forming apparatus using the intermediate transfer method, after the toner image is secondarily transferred from the intermediate transfer belt to the transfer material, toner (i.e., transfer residual toner) remains on the intermediate transfer belt. Thus, before toner images corresponding to the next image are primarily transferred onto the intermediate transfer belt, the transfer residual toner remaining on the intermediate transfer belt needs to be removed.
As a cleaning method for removing the transfer residual toner, a blade cleaning method is widely used. In the blade cleaning method, a cleaning blade as an abutment member that is placed downstream of the secondary transfer portion in the moving direction of the intermediate transfer belt and abuts the intermediate transfer belt scrapes off the transfer residual toner and collects the transfer residual toner in a cleaner case.
In such a blade cleaning method, the cleaning blade is often placed to constantly abut the intermediate transfer belt. In this case, after the image forming apparatus is used over a long period, a foreign substance such as paper dust may be caught in an abutment portion (i.e., a blade nip portion) between the cleaning blade and the intermediate transfer belt, whereby a cleaning failure may occur. Japanese Patent Application Laid-Open No. 2017-122852 discusses a configuration in which, to remove a foreign substance caught in a blade nip portion, when an image is not being formed, an intermediate transfer belt is moved in a direction opposite to that at a time of image formation.
In the configuration discussed in Japanese Patent Application Laid-Open No. 2017-122852, it is possible to suppress the occurrence of a cleaning failure by removing a foreign substance caught in a blade nip portion, but it is necessary to provide a driving mechanism for rotating the intermediate transfer belt backward. And thus, this may increase the cost of an image forming apparatus. Further, in a case where, to remove a foreign substance, the rotational direction of the intermediate transfer belt is switched to a direction opposite to that at a time of image formation, it is necessary to suspend image formation. And thus, this may reduce a throughput in a case where a foreign substance is removed when continuous printing is performed.